The present invention relates to a method and apparatus of two-degrees-of-freedom time difference comparison compensator for widely a feedback control system and, more particularly, a servo-system.
What is important in the feedback control system is not only the stability but also the quickness of responses, the stabilizability of perturbations and the robust stabilizability, all of which are desired to be fully versatile. The quickness of responses, and the stabilizability of perturbations or other several characteristics such as robust stabilizability are accompanied by physical conditions contracting one another. Thus, it is frequently urged to select what is to be stressed more the quickness of responses, the stabilizability of perturbations or other characteristics. The most powerful solution is the two-degrees-of-freedom control method of various modes, of which the most useful one is the I-PD control of the two-degrees-of-freedom control (as disclosed in "Optimum Parameters of Two-Degrees-of-Freedom PID Control System" written by Hidefumi Taguchi, Masateru Doi and Mitsuhiko Araki and belonging to Reports of Transaction of the Society of Instrument and Control Engineers, 23-9, 889/895 (1987)). According to this report, considerable effects are obtained in the quickness of responses, the stabilizability of perturbations and other characteristics. In the digital control using the optimal regulator, too, there are introduced into the countermeasures for the removal of steady state errors and perturbations the internal model principle (Bruce A. Francis: The multivariable Servomechanism Problem from the Input-Output View point, IEEE TRANSACTIONS ON AUTOMATIC CONTROL, Vol. AC-22, No. 3, 322/328 (1977)). By this introduction, satisfactory results are obtained in the quickness of responses, the stabilizability of perturbations and other characteristics. Generally, those characteristics are fairly excellent in the case of digital controls. Even if, however, the control system to be handled is a linear time invariant system, its design theory is so difficult to understand that it cannot be established to cope with many practical systems including the general non-linear elements. Still the worse, a room to be further improved is left in the digital control at the present stage.
Here, I, Nobuo Yamamoto has disclosed a related technology in U.S. Pat. No. 4,904,912 ("Control Mechanism Employing Internal Model Coordination Feedforward Method") and in U.S. patent application Ser. No. 182,432, now U.S. Pat. No. 4,953,076, entitled "Versatile Time Difference Comparison Compensation Method of Control System." However, the effect of the stabilizability of perturbations cannot be expected from both the versatile time difference comparison compensation method for the control system and the internal model coordination feedforward method of the control system. However, the effect of the stabilizability of perturbations cannot be expected from both the versatile time difference comparison compensation method for the control system and the internal model coordination feedforward method of the control system.
So, it cannot be said that the above-specified technologies of the prior art have succeeded in making adjustments for the supreme states while satisfying the quickness of responses, stabilizability of perturbations and other several characteristics simultaneously. It is the current practice to sacrifice and compromise some of those characteristics to some extent.